1. Field of the Invention
The invention relates to an aircraft door counter-balance system for aircraft doors which rotate about a horizontal axis.
2. Description of the Prior Art
Many aircraft presently in use have passenger doors which are mounted within the fuselage of the aircraft and rotate about a horizontal axis as the door is opened and closed. Particularly in the case of jet aircraft, wherein the passenger compartment of the aircraft is pressurized, the aircraft door is quite bulky and heavy. Typically, an aircraft door for such a jet aircraft may weigh approximately 200 pounds or more. Because of the bulky nature and weight of these aircraft doors, many problems are associated with the opening and closing of such doors by a person located either inside or outside the aircraft. For example, in the case of aircraft doors which rotate about a horizontal axis generally located at the lower portion of the door, there is a tendency for the door to develop momentum and swing rapidly downward as the door is opened, such that a person cannot control the movement of the door. Thus, in many instances, instead of being slowly opened, the door quickly swings downwardly until a portion of the door abuts a section of the fuselage. The section of the fuselage upon which the door abuts may be damaged by the force exerted by the weight of the door. In the case of pressurized jet aircraft, the cost associated with repairing a section of the fuselage can be extremely expensive.
When the door is opened from within the aircraft, there is a strong likelihood, in addition to possible damage to the aircraft, that the person opening the door may be seriously injured. As the door swings outwardly and downwardly into an opened position, the only portion of the door which a person may grasp is disposed along the lower portion of the door. Accordingly, the person does not have much leverage to counteract the forces exerted by the door if the door acquires momentum and swings down too rapidly. If that occurs the door has a tendency to pull the person opening the door outwardly from the aircraft. Consequently, the person is faced with the decision whether to release his grasp on the door, whereby the door may damage the aircraft fuselage, or to attempt to continue to grasp the door and risk being pulled headfirst from the aircraft onto the runway, which is located a substantial distance below the opening in the aircraft fuselage wherein the door is located.
If the door is opened by a person standing on the runway outside the aircraft, there is also a high likelihood that, in addition to possible damage to the aircraft, the person standing on the runway could be seriouly injured if the door were to rapidly swing open and strike him. If the person is merely standing in a position located underneath the door as one of the aircraft crew members attempts to open the door from within, he may likewise be injured by the door if it swings down rapidly.
Another problem associated with such aircraft doors occurs when trying to close the door. When the door is in an open position it overhangs the edge of the aircraft fuselage by a considerable amount and the center of gravity of the door is therefore located a considerable distance from the edge of the aircraft fuselage. Since the door must be grasped about the lower portion of the door in order to close it, a person located within the aircraft must bend down and extend his arms outwardly a considerable distance to grasp the lower portion of the door and then lift the weight of the door. However, this position is not conducive for exerting an effective lifting motion and, consequently, the weight of the door exerts a great strain upon a person's back. In the case wherein a person outside the aircraft on the runway attempts to close the door, the potential again exists for damaging the aircraft. Aside from the necessity of lifting the heavy door, the door, as it approaches a closed position has a tendency to slam into the fuselage, thereby possibly damaging the door and/or the fuselage.
One suggested solution for these problems has been to incorporate some type of counterbalance system disposed within the aircraft fuselage. For example, in the case of the North American Sabreliner jet aircraft, a counterbalance system is provided which provides a constant door counterbalancing force of approximately eighty pounds. However, the door of a Sabreliner weighs in excess of two hundred pounds, whereby a counterbalancing force in excess of one hundred twenty pounds must still be supplied in order to open and close the door. Additionally, the torque required to counterbalance the door is not a constant value, due to the manner in which the door rotates into its opened or closed position. Since the length of the moment arm, the distance between the door's horizontal axis of rotation and the door's center of gravity, is constantly changing, the torque necessary to counterbalance the weight of the door is likewise constantly changing.
Therefore, in addition to the disadvantage of not providing enough counterbalancing force, presently known counterbalancing systems do not provide a counterbalancing force which is varied dependent upon the position of the door as it is opened and closed. In the case of the North American Sabreliner, the constant eighty pound counterbalancing force does not adequately counterbalance the door whereby it may easily be opened and closed. As the door assumes a closed position the present counterbalance system tends to apply torque in excess of that required to counterbalance the door, whereby one must push against the door to prevent it from slamming into the aircraft fuselage. As the door assumes an opened position, the door tends to swing down rapidly and abut the fuselage, as previously described, since the present counterbalance system does not provide enough counterbalancing force.
Another disadvantage of known counterbalance systems for aircraft doors resides in their excessive weight. The more an aircraft weighs, the less payload the aircraft may accommodate. Therefore, many aircraft have either no door counterbalancing system or an inadequate counterbalancing system due to the aircraft designer's desire to minimize the weight of the aircraft.
Accordingly, prior to the development of the present invention, there has been no aircraft door counterbalance system available which is light in weight, exerts a variable torque upon the door, prevents damage to the aircraft door, and/or aircraft fuselage, prevents physical injury to those persons opening or closing the aircraft door, and enables fingertip operation when closing and opening the aircraft door. Therefore, the art has sought an efficient, light weight, safe, and inexpensive aircraft door counterbalance system for counterbalancing the weight of an aircraft door as it is opened and closed.